Multibeam Sonar Analysis of Dry Tortugas National...
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Multibeam Sonar Analysis of Dry Tortugas National Park HUGHES, Kristen and SAUTTER, Leslie Department of Geological and Environmental Geosciences, College of Charleston Dry Tortugas National Park was established in 1992 in order to maintain its unique and pristine marine habitat. Located ~112 km west of Key West, Florida, Dry Tortugas spans over 64,700 acres, with 99 % of its area under water. Unique coral communities with pinnacles, staghorn, and elkhorn corals are attracted to this tropical shallow water substrate. Multibeam sonar data were collected on the NOAA Ship Nancy Foster in September 2009 by investigators from the NOAA Florida Keys National Marine Sanctuary Coral Disease and Condition project. Bathymetric data were then processed using CARIS HIPS 7.0. The detailed seafloor maps and 3-D images created highlight some of the prominent features in the park, including various reef structures and east-west trending sand bodies. The reef platform is mainly composed of oolitic and coral sand deposits, with some carbonate muds and large sand bodies. The stratigraphy of Dry Tortugas ranges from sand and anthropogenic debris in the upper 1 to 15m of Holocene limestone. The most prominent layer is the Pleistocene Key Largo Limestone, which underlies Holocene deposits and is composed of fossilized patches of reef complexes and oolitic limestone. The living coral reefs are currently under threat of degradation due to vessel groundings and overuse. Multibeam analysis of Dry Tortugas provides a baseline and starting point for future efforts to preserve this National Park. NOAA Ship NANCY FOSTER METHODS Raw multibeam sonar data were acquired using Simrad EM1002 aboard the NOAA Ship Nancy Foster. Data were cleaned and processed using mapping software CARIS HIPS 7.0 Background Research was conducted to gain an understanding of the marine habitats characterizing the Dry Tortugas Area BACKGROUND The Dry Tortugas area is comprised of a group of islands located near the SW corner of the Florida Platform approximately 112 km west of Key West, Florida (Walter et. al 2002). The site is well protected from north and northwest seasonal storm activity by the shallow carbonate platform that underlies the subaerially exposed keys to the west and north (Walter et. al. 2002). This results in areas of thick accumulations of sediments of varying compositions, such as silt, sand, and shells (Walter et. al. 2002). The reefs of Dry Tortugas are thick in some locations, with accumulations of sediments up to 17 m, forming an elevated atoll-like rim (Thornberry 2005). Geologic activity in the Holocene consists of accumulation of coral reefs, carbonate muds, and sand deposits, which is controlled by geologic factors such as topography and climactic factors such as timing and rate of sea level rise, oceanic currents, and sediment facies (Thornberry 2005) Due to this unique location, Dry Tortugas protects unique coral communities including, pinnacles, staghorn and elkhorn corals (Thornberry 2005). DISCUSSION Multibeam data, surveyed ~112 km off the coast of Key West, revealing distinct carbonate features throughout the entire survey site. The unique carbonate environment provides a nutrient rich habitat for benthic organisms, comprising more than 99% of Dry Tortugas National Park (Thornberry 2005). Degradation is a constant threat for sea grass beds due to vessel groundings and overuse in the area as well as the slow steady rise in sea level (Thornberry 2005). It is important to understand these geologic features so that this pristine ecosystem can be preserved. Multibeam sonar analysis provides a good baseline for initiating preservation management of these special areas (NOAA). According to the data provided by NOAA in 2009, this survey site is rich with carbonate reef environments and atolls, providing multiple opportunities for rich marine ecosystems. Sites highlighted in this study indicate possible areas for further research where sediment samples and marine life survey could be useful for future protection of these distinctive environments. RESULTS: Multibeam sonar mapping of the survey area was performed during the 2009 research cruise onboard the NOAA Ship Nancy Foster , which revealed several submarine carbonate features: 1. On the north end of the survey site a Large platform that is ~1-1.5 km wide with ~10 m of relief was observed. 2. A series of isolated coral mounds that range from between 5 m tall to 10 m in average height was found within the central area of the survey site. 3. A massive platform is observed in the central survey site that is about 5-10 m in height and spans at least 1 km across. 4. Various patchy ‘reef like’ mounds was seen throughout the survey site. 5. One scarp like feature ~10 m deep towards the lower portion of the survey site was measured along profile a-a’ (figure. REFERENCES •Thornberry, T. L. 2005. Dry Tortugas National Park Geologic Resource Management Issues Scoping Summary. Colorado State University- Geologic Resource Evaluation •Walter, D.J., Lambert, D.N., Young, D.C. 2002. Sediment facies determination using acoustic techniques in a shallow-water carbonate environment, Dry Tortugas, Florida. Mar. Geol. 182, this issue. ACKNOWLEDGEMENTS Scott Donahue from NOAA for providing raw data and images and Josh Mode for training and assistance in CARIS 7.0 b’ a’ a ~5 m elevation change along scarp like feature- 3VE Fig. 4a Abrupt scarp like feature along profile a-a‘ using 2D view with depth scale b’ b Mound Features SE- 3 VE c’ c Sloping edge of the Carbonate Mound N-3 VE Fig. 4b Carbonate features along profile b-b’ in 2D view with depth scale Fig. 4c Profile c-c’ in 2D view with depth scale Figure 4. Three cross- sectional profiles depicting notable features of inertest within the Dry Tortugas Survey Site in 2D and 3D view. Figure 4a shows an interesting feature with a significant change in elevation within the carbonate environment. Figure 4b shows a group of mounds that have formed in the central are a of Dry Tortugas. Figure 4c runs along a large carbonate platform in the North side of the survey site. c c’ Fig. 1 Overview of Dry Tortugas bathymetry with cross- sectional profiles highlighting specific areas of interest. (meters) a’ a 2 b b’ 3 4 5 6 D 6 5 3 4 2 1 Fig. 3 Individual 3D images of Areas 1-6 listed on region map (Fig. 2). The images illustrate unique features within the Dry Tortugas Area. Images 1, 2, and 6 are relatively uniform across the surface while 3-5 have multiple carbonate mound features. Vertical exaggeration is 3x on all images. Fig. 2 Highlighted areas of interest are shown from North (top) Central (middle) and Southwest (lower) areas. Specific 3D images are enlarged in Figure 3, indicated by circled numbers 1-6. Arrows indicate direction of view. Cross-section profile lines are also indicated. North Central 44 42 12 14 16 18 20 28 26 24 22 30 32 34 36 38 40 (meters) 1 Shallow, flat ledge with ~10m of relief. Note the impressions along the top surface Shallow, flat ledge ~1.3km across from N-S and ~8m of relief. Isolated, circular feature partially connected to the main reef. Extensive reef area spanning ~6 km from N-S and ~3 km E-W Possible coral mounds found throughout the broad carbonate region. Large mound on the left has ~12 m of relief. Broad reef area with interspersed patchy coral mounds throughout. Relief in some areas reaches ~12 m Figure These images were take on the Nancy Foster in 2009 during mapping of the Dry Tortugas National Park 0 2000 4000 6000 8000 10000 m SURVEY AREA LOCATION
Transcript of Multibeam Sonar Analysis of Dry Tortugas National...
Multibeam Sonar Analysis of Dry Tortugas National ParkHUGHES, Kristen and SAUTTER, Leslie
Department of Geological and Environmental Geosciences, College of Charleston
Dry Tortugas National Park was established in 1992 in order to maintain its unique and pristine marine habitat. Located ~112 km west of Key West, Florida, Dry Tortugas spans over 64,700 acres, with 99 % of its area under water. Unique coral communities with pinnacles, staghorn, and elkhorn corals are attracted to this tropical shallow water substrate. Multibeam sonar data were collected on the NOAA Ship Nancy Foster in September 2009 by investigators from the NOAA Florida Keys National Marine Sanctuary Coral Disease and Condition project. Bathymetric data were then processed using CARIS HIPS 7.0. The detailed seafloor maps and 3-D images created highlight some of the prominent features in the park, including various reef structures and east-west trending sand bodies. The reef platform is mainly composed of oolitic and coral sand deposits, with some carbonate muds and large sand bodies. The stratigraphy of Dry Tortugas ranges from sand and anthropogenic debris in the upper 1 to 15m of Holocene limestone. The most prominent layer is the Pleistocene Key Largo Limestone, which underlies Holocene deposits and is composed of fossilized patches of reef complexes and oolitic limestone. The living coral reefs are currently under threat of degradation due to vessel groundings and overuse. Multibeam analysis of Dry Tortugas provides a baseline and starting point for future efforts to preserve this National Park.
NOAA Ship NANCY FOSTER
METHODS
Raw multibeam sonar data were acquired using Simrad EM1002 aboard the NOAA Ship Nancy Foster.
Data were cleaned and processed using mapping software CARIS HIPS 7.0
Background Research was conducted to gain an understanding of the marine habitats characterizing the Dry Tortugas Area
BACKGROUND
The Dry Tortugas area is comprised of a group of islands located near the SW corner of the Florida Platform approximately 112 km west of Key West, Florida (Walter et. al 2002).
The site is well protected from north and northwest seasonal storm activity by the shallow carbonate platform that underlies the subaerially exposed keys to the west and north (Walter et. al. 2002). This results in areas of thick accumulations of sediments of varying compositions, such as silt, sand, and shells (Walter et. al. 2002).
The reefs of Dry Tortugas are thick in some locations, with accumulations of sediments up to 17 m, forming an elevated atoll-like rim (Thornberry 2005).
Geologic activity in the Holocene consists of accumulation of coral reefs, carbonate muds, and sand deposits, which is controlled by geologic factors such as topography and climactic factors such as timing and rate of sea level rise, oceanic currents, and sediment facies (Thornberry 2005)
Due to this unique location, Dry Tortugas protects unique coral communities including, pinnacles, staghorn and elkhorn corals (Thornberry 2005).
DISCUSSION
Multibeam data, surveyed ~112 km off the coast of Key West, revealing distinct carbonate features throughout the entire survey site. The unique carbonate environment provides a nutrient rich habitat for benthic organisms, comprising more than 99% of Dry Tortugas National Park (Thornberry
2005). Degradation is a constant threat for sea grass beds due to vessel groundings and overuse in the area as well as the slow steady rise in sea level (Thornberry 2005). It is important to understand these geologic features so that this pristine ecosystem can be preserved.
Multibeam sonar analysis provides a good baseline for initiating preservation management of these special areas (NOAA). According to the data provided by NOAA in 2009, this survey site is rich with carbonate reef environments and atolls, providing multiple opportunities for rich marine
ecosystems. Sites highlighted in this study indicate possible areas for further research where sediment samples and marine life survey could be useful for future protection of
these distinctive environments.
RESULTS:
Multibeam sonar mapping of the survey area was performed during the 2009 research cruise onboard the NOAA Ship Nancy Foster , which revealed several submarine carbonate features:
1. On the north end of the survey site a Large platform that is ~1-1.5 km wide with ~10 m of relief was observed.
2. A series of isolated coral mounds that range from between 5 m tall to 10 m in average height was found within the central area of the survey site.
3. A massive platform is observed in the central survey site that is about 5-10 m in height and spans at least 1 km across.
4. Various patchy ‘reef like’ mounds was seen throughout the survey site.
5. One scarp like feature ~10 m deep towards the lower portion of the survey site was measured along profile a-a’ (figure.
REFERENCES
•Thornberry, T. L. 2005. Dry Tortugas National Park Geologic Resource Management Issues Scoping Summary. Colorado State University-Geologic Resource Evaluation•Walter, D.J., Lambert, D.N., Young, D.C. 2002. Sediment facies determination using acoustic techniques in a shallow-water carbonate environment, Dry Tortugas, Florida. Mar. Geol. 182, this issue.
ACKNOWLEDGEMENTS
Scott Donahue from NOAA for providing raw data and images and Josh Mode for training and assistance in CARIS 7.0
b’
a’
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~5 m elevation change along scarp like feature- 3VE
Fig. 4aAbrupt scarp like feature along profile a-a‘ using 2D view with depth scale
b’
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Mound Features SE- 3 VE
c’c
Sloping edge of the Carbonate Mound N-3 VE
Fig. 4bCarbonate features along profile b-b’ in 2D view with depth scale
Fig. 4cProfile c-c’ in 2D view with depth scale
Figure 4.
Three cross-sectional profiles depicting notable features of inertest within the Dry Tortugas Survey Site in 2D and 3D view. Figure 4a shows an interesting feature with a significant change in elevation within the carbonate environment. Figure 4b shows a group of mounds that have formed in the central are a of Dry Tortugas. Figure 4c runs along a large carbonate platform in the North side of the survey site.
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Fig. 1Overview of Dry Tortugas bathymetry with cross-sectional profiles highlighting specific areas of interest.
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Fig. 3 Individual 3D images of Areas 1-6 listed on region map (Fig. 2). The images illustrate unique features within the Dry Tortugas Area. Images 1, 2, and 6 are relatively uniform across the surface while 3-5 have multiple carbonate mound features. Vertical exaggeration is 3x on all images.
Fig. 2Highlighted areas of interest are shown from North (top) Central (middle) and Southwest (lower) areas. Specific 3D images are enlarged in Figure 3, indicated by circled numbers 1-6. Arrows indicate direction of view. Cross-section profile lines are also indicated.
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Shallow, flat ledge with ~10m of relief. Note the impressions along the top surface
Shallow, flat ledge ~1.3km across from N-S and ~8m of relief.
Isolated, circular feature partially connected to the main reef.
Extensive reef area spanning ~6 km from N-S and ~3 km E-W
Possible coral mounds found throughout the broad carbonate region. Large mound on the left has ~12 m of relief.
Broad reef area with interspersed patchy coral mounds throughout. Relief in some areas reaches ~12 m
FigureThese images were take on the Nancy Foster in 2009 during mapping of the Dry Tortugas National Park
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SURVEY AREA LOCATION
